Cold hardiness & minimum temperature

Is African Cornflag (Chasmanthe aethiopica)cold hardy? Hardiness zone & min temp

Also called African cornflag, Small cobra lily, Pennant flower.

More about african cornflag

About African Cornflag

Chasmanthe aethiopica · also called African cornflag, Small cobra lily · flowering

African cornflag is a vigorous, winter-growing cormous perennial from the fynbos and coastal scrub of South Africa, producing tall, sword-like leaves and arching spikes of vivid orange-red tubular flowers in late winter to early spring. In mild, frost-free climates it grows outdoors year-round; elsewhere the corms must be lifted and stored dry over winter. The single most critical care requirement is strict summer dormancy — corms left in wet soil during their dry-season rest will rot. Chasmanthe aethiopica is not listed as toxic by the ASPCA but, as a precaution with corms of uncertain status, treat as mildly toxic to pets.

Cold limit: USDA 8-10 · RHS H3 (-5 to 30°C)

Watch for — Aphids on flower spikes: Aphid colonies congregate on emerging flower stems in late winter, weakening growth and disfiguring blooms. Inspect from midwinter onwards and treat with insecticidal soap spray or neem oil at the first sign of infestation.

What african cornflag's hardiness rating actually means

African Cornflag is half-hardy (RHS H3). It survives a mild winter outdoors in a sheltered spot, but a hard frost kills it — so in colder zones it is lifted, potted, or grown as a tender plant. Its RHS rating of H3 means: Half-hardy — comes through mild UK winters outside but is killed by a hard freeze. On the US scale that maps to USDA 8-10 — the zones where it can be left outdoors year-round.

New to these scales? The USDA hardiness zone map explained covers how the zone numbers work, and you can find your own zone with the zone finder.

Minimum temperature — and what happens below it

Minimum survivable temperature is roughly about −5 to 1 °C — a light, short frost only. African Cornflag shrugs off cold nights but a real, sustained freeze will kill it.

Concretely, for african cornflag as it gets too cold:

Down to roughly about −5 to 1 °C it copes, especially if dry and sheltered.
A sustained hard frost collapses the top growth; whether it returns depends on whether the roots, crown or tubers froze.
Wet cold is far more lethal than dry cold for this plant — soggy, frozen soil is the usual killer.

Can african cornflag go outside or overwinter — and where?

It can live outside year-round only in the mildest, most sheltered part of USDA 8-10 or a frost-free UK microclimate.
In colder zones, grow it in a pot you can move under cover, or lift its tubers/roots and store them frost-free over winter.
A south-facing wall, free-draining soil and a dry winter position can push it a full zone hardier than the books suggest.

Work back from your local frost dates with the frost-date calculator: the last spring frost and first autumn frost are what really decide when african cornflag can be outside. US growers can check USDA zones; UK growers should use the RHS hardiness ratings, which match the H3 figure above.

Frost protection for borderline african cornflag

African Cornflag is right on a hardiness edge in many gardens, so if you are pushing it, these measures buy it the margin it needs:

Mulch the crown or root zone deeply with bark, straw or leaf-mould before the first hard frost.
Move container plants against a warm wall or into an unheated but frost-free porch or greenhouse.
Fleece the top growth on the coldest nights, and keep it on the dry side — dry roots survive cold far better than wet ones.
Lift dahlia-type tubers or tender crowns after the first light frost blackens the foliage and store them somewhere cool but frost-free.

African Cornflag hardiness — frequently asked questions

Is african cornflag cold hardy?

African Cornflag is half-hardy (RHS H3). It survives a mild winter outdoors in a sheltered spot, but a hard frost kills it — so in colder zones it is lifted, potted, or grown as a tender plant. Borderline outdoors. In its mild end of USDA 8-10 (and sheltered UK gardens) african cornflag can stay out; in colder areas it must be lifted, brought in, or treated as a frost-tender plant.

What is the minimum temperature african cornflag can survive?

Minimum survivable temperature is roughly about −5 to 1 °C — a light, short frost only. African Cornflag shrugs off cold nights but a real, sustained freeze will kill it.

What hardiness zone is african cornflag?

African Cornflag is rated USDA 8-10 and RHS H3 — Half-hardy — comes through mild UK winters outside but is killed by a hard freeze.

Can african cornflag survive winter outside?

It can live outside year-round only in the mildest, most sheltered part of USDA 8-10 or a frost-free UK microclimate. In colder zones, grow it in a pot you can move under cover, or lift its tubers/roots and store them frost-free over winter. A south-facing wall, free-draining soil and a dry winter position can push it a full zone hardier than the books suggest.

How do I protect african cornflag from frost?

Mulch the crown or root zone deeply with bark, straw or leaf-mould before the first hard frost. Move container plants against a warm wall or into an unheated but frost-free porch or greenhouse. Fleece the top growth on the coldest nights, and keep it on the dry side — dry roots survive cold far better than wet ones. Lift dahlia-type tubers or tender crowns after the first light frost blackens the foliage and store them somewhere cool but frost-free.